Wall Street entrepreneur and financier Thomas Kaplan is seen on the left in a file photo from March 2008 and his missing nephew, millionaire Guma Aguiar is seen on right in a August 2009 file photo. The two were locked in a long-running legal battle over money before Aguiar went missing in June 2012.

Aguiar and Kaplan have been in a nasty legal battle since 2009 over the $2.5 billion sale of their Texas-based energy company. The two have been at odds about the division of the money from the sale, and Aguiar was convinced that his uncle was trying to kill him.

Aguiar, 35, was last seen on June 19 in Fort Lauderdale, Fla. Early the next morning, his 31-foot fishing boat washed up on a Fort Lauderdale beach with the engine running and lights on, but with no sign of its Brazilian-born owner.

Aguiar's mother Ellen Aguiar and wife Jamie Aguiar filed a flurry of legal motions in a battle over control of his assets, valued at over $100 million, in the week following his disappearance.

A court decided last week, after help from a pair of rabbi mediators, that control would be given to the Northern Trust, a wealth management company selected by Aguiar to take care of his assets should anything ever happen to him.

Kaplan, 49, remained mum throughout the very public tug-of-war until he quietly filed a motion last week to preserve all electronic data and communication devices belonging to both Guma and Ellen Aguiar. Kaplan and his sister Ellen Aguiar have also been in their own financial battle.

In the filing, Kaplan's attorneys wrote that Aguiar "disappeared under suspicious circumstances" and that "the parties remain hopeful that Aguiar is alive."

"The parties and the Court have an interest in determining Aguiar's whereabouts and the circumstances surrounding his disappearance," the filing said.

Aguiar and Kaplan have a bitter history with email. In 2009, Kaplan accused Aguiar of hacking into his email and accessing all of his private information.

This was the beginning of a nasty legal battle that divided the family. Court documents state that Aguiar suffered from "severe bipolar disorder and psychosis" and Aguiar was increasingly convinced that his uncle was trying to kill him.

"Aguiar's psychosis manifested itself in both grandiose and paranoid delusions," a court document from 2010 reads. "With respect to his paranoid delusions, Aguiar has stated on multiple occasions that Kaplan was trying to kill him. Aguiar believes that he has been poisoned, the he was shot in the back from a helicopter, that snipers have been following him and that the medical staff at an Israeli hospital were injecting him with poison in order to kill him."

Kaplan's motion requested that any electronic data related to Aguiar's disappearance, including any communication between Guma and Ellen Aguiar, be preserved.

A few days later, a Florida judge ordered that the data and devices be preserved for 180 days. The judge's order includes text messages, emails, phone logs, files accessed, voicemail and electronically stored faxes tied to all of the mother and son's phone numbers and email addresses.

Battle for Missing Millionaire's Fortune Resumes in Court Today

The interest in Aguiar's electronic communication has been building ever since his cell phone and wallet were found on his washed-up boat.

Ellen Aguiar had the items for a period of time before giving them to her attorney who turned them back over to police, but Jamie Aguiar's legal team has raised questions about the circumstances surrounding her possession of the items.

They alleged that Ellen Aguiar had persuaded police to hand over the phone and "made a few phone calls and possibly deleted critical voice and/or text messages" before returning the phone.

"Ellen Aguiar never asked for the phone," he said. "She never asked for the wallet. That's complete and utter fantasy."

At a hearing today, a Florida judge appointed Northern Trust with conservatorship over all of Aguiar's trust assets, Florida attorney Thomas Panza was appointed to manage all of Aguiar's non-trust assets, and Ft. Lauderdale Mayor Jack Seiler was appointed conservator over all litigation.

Kaplan's attorney did not respond to request for comment from ABCNews.com.